The end face of known test apparatus of this kind is either straight or composed of angled sections, so that it may be straight or, considered as a whole, curved, for example, in the direction of movement of the test material, that is, for example, the yarn, roving or sliver. This applies particularly if the test apparatus is composed of modules which each occupy a section of the end face. Such test apparatus is shown and described, for example, in Great Britain patent GB 2 192 722, the disclosure of which is incorporated herein by reference.
It is also usual to provide guides for guiding the yarn, roving or sliver separately in two directions, namely: parallel and perpendicular to the end face. The end face may be divided into different zones of action such as, e.g. a test or measurement zone, in which properties of the yarn, roving or sliver are tested or measured, a guide zone, in which means for orienting and guiding the yarn, roving or sliver are provided, and into a drive zone, in which means for driving or moving the yarn, roving or sliver are provided. These zones of action are usually laterally staggered, so that the test material follows a variable, bent path (viewed in the direction of the end face). Or, in other words, the yarn, roving or sliver is directed by guides in the region of the measurement zone into a path which outside of this region adopts a different course which does not constitute a natural continuation of the path in this region or in the measurement zone.
The disadvantages which this arrangement entails lie in the fact that in this case guides always produce deflections which may affect the properties of the yarn, roving or sliver. For example, the hairiness of a yarn may be changed to a greater or lesser degree according to the angle at which the yarn loops round the guide and according to the radius of the guide. Furthermore, the zones of action which are to follow one another in the longitudinal direction of the yarn, roving or sliver must be laterally staggered such that the action of guides of preceding and following zones of action is not impaired. This either results in the yarn, roving or sliver being laterally displaced by a certain amount or deflected for each zone of action or in the necessity of providing a particularly large number of guides. In addition, the guides are subjected to high loads and in turn load and deform the cross section of the yarn, roving or sliver.